1. Field of the Invention
The present invention relates to a uric acid sensing device, and in particular relates to a separative extended gate field effect transistor based uric acid sensing device.
2. Description of the Related Art
Uric acid is one of the metabolism products of purine (one important constituent of a genetic material such as nucleic acid) and can be produced through autosynthesis, tissue dissolution and nucleoprotein ingestion by a human body. Purine is metabolized through the liver to form uric acid, and uric acid is metabolized to drain from the kidney. Uric acid concentrations in blood increase when the human body production rate is faster than the kidney draining rate. In the U.S.A., medical reports indicate that when uric acid concentrations in patients blood are over the standard concentration about 0.1 mg, morbidity of cardiopathy increases more than high cholesterol and hypertension. Additionally, when using a diuretic to cure hypertension, uric acid concentrations will increase for patients with higher than 0.1 mg of uric acid concentration in their blood. The high concentrations of uric acid and blood sugar in blood cause pathological symptoms for humans. Thus, a biosensor with high sensitivity, easy operation and real-time response to test concentrations of uric acid in blood has been developed.
An ion-sensitive field effect transistor (ISFET) is applied to an electrochemical sensing device. The structure of a separative extended gate field effect transistor (SEGFET) has been developed from the ISFET. In contrast with the ISFET using high impedance material as its sensing thin film, the ion sensing thin film of the SEGFET is fabricated by low impedance material for relatively better conductivity and sensitivity. Therefore, high impedance material is suitable for ISFETs, but not for SEGFETs. Meanwhile, the SEGFET structure comprises a MOSFET which retains a metal gate electrode and utilizes a signal wire to connect the separative ion sensing film and the field effect transistor.
In 1983, J. Van der Spiegel et al developed an extended gate chemical sensitive field effect transistor, which used a plane array structure, including four sensing parts deposited of different materials such as IrOx, LaF3, AgCl and Ag2S to from the sensing thin films for detecting four kinds of ions, H+, F−, Cl− and Ag+ (J. Van der Spiegel, I. Lauks, P. Chan D. Babic, 1983, “The extended gate chemical sensitive field effect transistor as multi-species microprobe”, Sensors and Actuators B, Vol. 4, pp. 291-298).